The manufacture of master cylinders is usually achieved through either sand or permanent mold casing of molten metal to a particular shape. When the molten metal has cooled the sand or core is removed from any cavities therein. As the molten metal cools, a uniform dense surface is created on the periphery of the casting; however, some voids may occur internally. Thereafter when the casting is machined to its final tolerance, such as the master cylinder housing disclosed in U.S. Pat. No. 3,701,257, it is possible that some of the voids may be exposed in the pressurizing chambers. If a master cylinder were assembled having a void exposed in the bore, in addition to providing a possible leak path for the high pressure fluid in the pressurizing chamber, it is possible to damage the seals as they are moved past such voids. Thus once a void is exposed in the bore through machining for safety, the master cylinder casting is automatically scrapped. It is estimated that between 2 and 5 percent of the castings manufactured during any given period of time are scrapped because of the potential hazards created by the exposure of voids during machining.
It has been observed that die casting, when compared with sand or permanent mold castings, produces a smoother surface finish with thinner dimensions and closer manufacturing tolerances.